Nonaqueous electrolyte batteries using a lithium ion are expected to be applied to on-vehicle applications such as micro-hybrid vehicles and idling stop systems, stationary applications, and the like since they have features such as a high energy density and a long lifespan.
An olivine-type phosphate compound as a positive electrode active material exhibiting excellent high temperature durability and a titanate metal oxide as a negative electrode active material have been paid attention in a nonaqueous electrolyte battery, respectively.
In the positive electrode active material, lithium iron phosphate having an olivine structure exhibits excellent lifetime characteristics since it has a stable crystal structure and a relatively low absorbing and releasing potential of lithium ion of about 3.4 V (vs. Li/Li+).
In the negative electrode active material, lithium titanate having a spinel structure has advantages such as excellent cycle characteristics and high safety since the volume thereof does not change in association with the charge and discharge reaction.
The cell using a titanate metal oxide as the negative electrode has a problem that the cell capacity of the nonaqueous electrolyte battery significantly deteriorates by the influence of SOC deviation or the like since the operating voltage is flat, which is a feature of a two-phase coexisting system and a side reaction by the functional group on the surface of the negative electrode active material generates a gas.